Effects of Vibrio cholerae recombinant strains on rabbit ileum in vivo. Enterotoxin production and myoelectric activity

Clostridium perfringens epsilon toxin inhibits the gastrointestinal transit in mice

Epsilon toxin produced by Clostridium perfringens type B and D is a potent toxin that is responsible for a highly fatal enterotoxemia in sheep and goats. In vitro, epsilon toxin produces contraction of the rat ileum as the result of an indirect action, presumably mediated through the autonomic nervous system. To examine the impact of epsilon toxin in the intestinal transit, gastric emptying (GE) and gastrointestinal transit (GIT) were evaluated after intravenous and oral administration of epsilon toxin in mice. Orally administered epsilon toxin produced a delay on the GIT. Inhibition of the small intestinal transit was observed as early as 1 h after the toxin was administered orally but the effects were not observed after 1 week. Epsilon toxin also produced an inhibition in GE and a delay on the GIT when relatively high toxin concentrations were given intravenously. These results indicate that epsilon toxin administered orally or intravenously to mice transitorily inhibits the GIT. The delay in the GIT induced by epsilon toxin could be relevant in the pathogenesis of C. perfringens type B and D enterotoxemia.

Novel gut afferents: Intrinsic afferent neurons and intestinofugal neurons

Information about the conditions of all tissues in the body is conveyed to the central nervous system through afferent neurons. Uniquely amongst peripheral organs, the intestine has numerous additional afferent neurons, intrinsic primary afferent neurons that have their cell bodies and processes in the enteric plexuses and do not project to the central nervous system. They detect conditions within the gut and convey that information to intrinsic reflex pathways that are also entirely contained inside the gut wall. Intrinsic primary afferent neurons respond both to the presence of material in the gut lumen and to distension of the gut wall and initiate reflex changes in contractile activity, fluid transport across the mucosa and local blood flow. They also function as nociceptors that initiate tissue-protective propulsive and secretory reflexes to rid the gut of pathogens. The regulation of excitability of intrinsic primary afferent neurons is through multiple ion channels and ion channel regulators, and their excitability is critical to setting the strength of enteric reflexes. The intestine also provides afferent signals to sympathetic pre-vertebral ganglia. The signals are conveyed from the gut by intestinofugal neurons that have their cell bodies within enteric ganglia and form synapses in the sympathetic ganglia. Intestinofugal neurons form parts of the afferent limbs of entero-enteric inhibitory reflexes. Because the unusual afferent neurons of the small intestine and colon make their synaptic connections outside the central nervous system, the neurons and the reflex centres that they affect are potential targets for non-central penetrant therapeutic compounds.

Intestinal motor disorders associated with cyclical bacterial overgrowth in a rat model of enteritis

The aims of this study were: 1) to obtain an experimental model reproducing the characteristics of chronicity and spontaneous relapses found in inflammatory bowel disease (IBD) and 2) to correlate these changes with intestinal motility and bacteria translocation. For this purpose, two groups of Sprague-Dawley rats were used: a treated group that received two subcutaneous injections of indomethacin (7.5 mg/kg) 48 h apart and a control group that received saline. Blood leukocytes, TNF, and fecal parameters were monitored for 90 days after treatment. In treated rats, a cyclic oscillation of blood leukocytes and TNF concomitant with an inverse correlation of fecal output was observed. Treated rats were then selected either during their highest or lowest blood leukocyte values for motor activity and microbiological evaluation. Controls were obtained in age-matched rats. Rats with high leukocyte levels showed a decrease of motor activity. In contrast, animals with low leukocyte levels presented hypermotility. Bacterial overgrowth accompanied by bacterial translocation was found in the group with high leukocytes, whereas no differences were observed between the control and indomethacin groups during the lowest leukocyte phase. We obtained a model of IBD characterized by a chronic cyclic oscillation of intestinal motility, flora, and inflammatory blood parameters. During the high-leukocyte stage, motor activity decrease is related to bacterial translocation. This phase is followed by a reactive one characterized by hypermotility associated with a decrease in both bacterial growth and leukocytes. However, as in IBD, this reaction seems unable to prevent a return to relapse.

Cloning, expression and characterization of the CHO cell elongating factor (Cef) from Vibrio cholerae O1

CHO cell-elongating factor (Cef) is a recently identified putative virulence factor of Vibrio cholerae. Our previous studies show that this 85 kDa protein elongates CHO cells, causes fluid accumulation in suckling mice and has esterase activity. In this study, the cef gene was cloned in Escherichia coli using a yeast vector and subsequently expressed in the yeast Pichia pastoris. The cef genes from V. cholerae candidate vaccine strains JBK 70 and CVD 103-HgR were sequenced and found to be nearly identical (100 and 99.9% respectively) with an open reading frame (ORF) from the published sequence of V. cholerae N16961. Cloned toxin was purified to homogeneity in 3 steps using anion exchange, hydrophobic interaction and gel filtration chromatography. The size of cloned Cef on SDS-PAGE gels was 114 kDa. The increased size was probably due to glycosylation by the yeast since cloned protein reacted strongly with a glycoprotein stain. The cloned protein could not be directly sequenced, but when treated with trypsin, yielded a protein fragment with an amino acid sequence that matched the sequence predicted for the Cef protein. The purified cloned protein had esterase and CHO cell activity, but no suckling mouse activity.

Effect of cloned Salmonella typhimurium enterotoxin on rabbit intestinal motility

We analysed the small intestine myoelectric responses of anesthetized New Zealand albino rabbits to Escherichia coli lysates containing an entertoxin cloned from Salmonella typhimurium. Migrating action potential complex, which consisted of rapid bursts of actions potentials and secretion of fluid, was observed only in ileal loops, injected with the enterotoxin-containing lysate. Migrating action potential complex produced by Stn usually propagated aborally, which was typical of cholera toxin, but orad or bidirectional propagation occurred from a single point of origin when activity was intense. Cell lysates from an E. coli clone containing vectors alone, as well as proximal control segments injected with phosphate-buffered saline, gave neither a change in motility nor fluid secretion. These results show that Stn caused dramatic changes in intestinal motility and substantial fluid production.